Travelling in Time: How to Wholly Exist in Two Places at the Same Time
Miller (Kristie)
Source: Canadian Journal of Philosophy, Vol. 36, No. 3 (Sep., 2006), pp. 309-334
Paper - Abstract

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Author’s Introduction

  1. It is possible to wholly exist at multiple spatial locations at the same time. At least, if time travel is possible and objects endure, then such must be the case. To accommodate this possibility requires the introduction of a spatial analog of either relativising properties to times - relativising properties to spatial locations - or of relativising the manner of instantiation to times - relativising the manner of instantiation to spatial locations. It has been suggested, however, that introducing irreducibly spatially relativised or spatially adverbialised properties presents some difficulties for the endurantist. I will consider an objection according to which embracing such spatially relativised properties could lead us to reject mereology altogether in favour of a metaphysics according to which objects are wholly present at every space-time point at which they exist. I argue that although such a view is coherent, there are some good reasons to reject it. Moreover, I argue that the endurantist can introduce spatially relativised or adverbialised properties without conceding that objects lack spatial parts. Such a strategy has the additional advantage that it allows the endurantist not only to explain time travel, but also to reconcile our competing intuitions about cases of fission.
  2. The possibility of travelling back in time to a period in which one's earlier self or one's ancestors existed, raises a number of well-worn problems: See:- In this paper I am concerned with only one of these: how is it that an object can travel back in time to meet its earlier self, thus existing at two different spatial locations at one and the same time?
  3. Four-dimensionalis have an easy answer to this question. Or at least, the vast majority of four-dimensionalists, who hold that objects persist by perduring - perdurantists - have an easy answer to this question. See:- Perdurantists1 hold that persisting objects are four-dimensional space-time worms that are at each time at which they exist, partly present in virtue of having some part - a temporal part - present at that time. Though four-dimensional objects are of course self-identical, no two parts of a four-dimensional whole are strictly identical. So we can explain how I can meet myself in the past, by noting that my younger self and my older self are two different temporal parts of one and the same four-dimensional whole that is me. Thus we can reconcile the intuition that the younger and older selves are both me, with the intuition that they are distinct and have different properties ("Lewis (David) - On the Plurality of Worlds", 1976).
  4. Three-dimensionalists or endurantists, however, hold that persisting objects have only three dimensions: they are not extended in time and do not persist by having temporal parts. Rather, three-dimensional objects endure (hence endurantists): they are wholly present whenever they exist. See:- Thus if some enduring object O exists through T, then for every time t and t* in T, O wholly exists at t and t* and is strictly identical to itself at2 each of these times. For the endurantist, then, my younger self and I are not parts of the persisting object that is me, but rather, my younger self and I are strictly identical. But then the possibility of time travel raises the spectre of the same object wholly existing in two locations at the same time.
  5. Plan:
    • In section II, I begin by briefly outlining the manner in which the Perdurantist accounts for the possibility of a time travelling self meeting his or her younger self.
    • In section III, I explain how the endurantist will need to make use of spatially relativised properties, and I consider a minor worry that Ted Sider has with this proposal.
    • In section IV, I consider whether the introduction of irreducibly spatially relativised properties paves the way for rejecting the existence of all parts, temporal and spatial alike. I consider a view I call mega-endurantism, according to which not only are objects wholly present at every temporal instant at which they exist, but are also wholly present at every space-time point at which they exist. This, then, is the view that objects endure across space as well as time. While this view is an interesting one that raises some pertinent questions for the endurantist, ultimately I argue that it has too high a cost.
    • Moreover, as I argue in section V, the introduction of spatially relativised properties does not force the endurantist in general to reject mereology.
    • Though there are perhaps some costs to the idea that an object can be wholly present at multiple spatial locations at the same time, there are, as I argue in section VI, also some benefits. Chief among these is that intuitions regarding cases of fission wherein an object 'splits' into two qualitatively identical objects, can best be explained by holding that the same object can be wholly present at multiple spatial regions. This is important because one major benefit cited to perdurantism is that it allows the reconciliation of what appear to be contradictory intuitions regarding cases of fission, in a way that endurantism is unable. Such need no longer be the case.
Sections
  1. Introduction
  2. Worldlines and Worms
  3. Time Travelling Endurantists
  4. Mereological Abstinence
  5. Re-instating parts
  6. Fission Explained
  7. Conclusion
Author’s Conclusion
  1. So the possibility of time travel need not faze the endurantist. Indeed, consideration of such a possibility opens the door for a new way of making sense of cases of fission.
  2. It turns out that objects can be wholly present at multiple spatial regions at the same time, and why should this be surprising, after all, objects can be wholly present at multiple temporal locations at the same spatial location.



In-Page Footnotes

Footnote 1: I distinguish perdurantism from four-dimensionalism on the grounds that four-dimensionalism is the thesis that persisting objects are temporally extended: they have four dimensions. This need not entail that such objects persist by having temporal parts, though this is by far the most usual view.

Footnote 2:

Text Colour Conventions (see disclaimer)

  1. Blue: Text by me; © Theo Todman, 2017
  2. Mauve: Text by correspondent(s) or other author(s); © the author(s)



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